Name:Class:Date:

Issuesanddecisions 4

Shouldalienspeciesbeintroducedtoecosystems?

eliberatelyoraccidentally,manyspeciesofplantsandanimalshavebeentransportedallovertheworld

throughglobaltrade.Nativespeciesexistinanecosysteminabalancedrelationshiptooneanother.Whenspeciesaretakenfromtheirnativehabitatsandtransplantedinnewecosys-tems,thesespeciescanseriouslydisrupttheecosystemstheyinvade.Transportedspeciesarecommonlyreferredtoasalienspecies.

Alienspeciesaredisruptivebecausetheecosystemstheyinvadeoftenhavenowaytocontrolthem.Inbalancedecosystems,predatorsandpreyactascontrolsoneachother’spopula-tions.Anecosystemmayhavenopredatorthatcancontrolthepopulationofanintroducedalienspecies.

Alienspeciesmayalsocarryaliendiseases.Plantandanimalspeciesusuallydevelopsome resistancetodiseasesthatnaturallyoccur withintheirhabitats.Buttheyusuallyhavenoresistancetoforeigndiseases,andsoareeasilykilledbythem.Finally,intheabsenceofpreda-tors,alienspeciesareoftenabletooutcompetenativespeciesforresources,suchasfoodorspace.Nativespecies maythen bepushed outoftheirhabitat,andtheirpopulationsmay decline,sometimestothepointofextinction.

AccidentalInvasions

Californiaisamajorprovideroffreshpro-duceformuchoftheUnitedStates.IfyouhaveeverdriventoCaliforniafromanotherstate,youwereprobablystoppedattheborderandaskedbyanofficialifyouhadanyfruitsorveg-etablesinyourcar.TheofficialprobablyaskedyoutogiveupanyfreshproduceyouwerecarryingtoensurethatyouwerebringinginnoMediterraneanfruitflies.Thesefruitflies,called“Medflies”forshort,poseamajorthreattoCal-iforniacrops.

Medflies,nativetotropicalAfrica,landedinHawaii in 1910.These insects soonfound theirwaytoCalifornia’sfarmfields,wheretheybegan todevastate crops.Farmers became

involvedinafierceandcontinualbattle,usu-allyinvolvingtheuseofpesticides,toeliminatetheseinsects.TheMedfly,however,stillperiodi-callyturnsupamongthefruitsandvegetablesgrowinginCalifornia.

Otherforeignspecieshavedevastatedtheforests oftheUnitedStates.Chestnutblight,adiseasethathasendangeredtheAmericanchestnuttree,iscausedbyafungusthatgrowsbeneaththebarkofthetree.ItwasfirstnotedinNew Yorkin1904.Thefungussporesproba-blyenteredNewYorkharborunderthebarkoftreesthatwereimportedfromAsia.By1950,

3.5billionchestnuttreeshadbeenafflictedwiththeblight.

Anotherwayalienspecieshavetraveledtoforeignlandsisoncargoshipsusedininterna-tionaltrade.Whencargoshipsleavetheirhomeport,theyoftentakeonupto190millionlitersofwater,whichtheykeepinballastcontainers.Thisballasthelpstheshipsstaybalancedandstableduringoceanvoyages.Whentheshipsreachtheirdestination,theyreleasewaterfrom theirballastsintotheforeignharbor.Someoftheworld’smostseriousalien-speciesproblemshavebeen causedby “stowaways”in shipbal-lasts.Forexample,scientistssampledballastwaterfrom159JapanesecargovesselsthathaddockedinOregon.Theyfound370non-nativeorganismsswarmingintheballasttanks,includingfish,plankton,crabandclamlarvae, worms,shrimp,snails,andjellyfish.Allthesealienspeciesweretobeflushedoutofthebal-lasttanksandintothewatersofOregon’s

CoosBay.

Theaboveexamplesdescribeonlyafewoftheaccidentalarrivalsofalienspeciesandsome oftheireffectsonnativespecies.Thesespecies’introductionresultedinseriousdisruptionsofthelocalecosystemsinvaded.Notallalienspecies,however,aretheresultofaccidents.

IntroducingAlienSpeciestoIncreaseProfits

Sometimesalien speciesare introduceddeliberatelyintoanareatobenefitanindustry

becausetheyhaveausefulgenetictrait.Honey- beesareanintroducedspecies,broughttotheUnitedStatesfromEurope.Themoreaggres-siveandmoreproductivewildAfricanbeeswereimportedintoBrazilin 1956.ScientistshopedthehoneybeesandAfricanbeeswouldinterbreed,creatingamoreproductive,yetgentlehybrid.BecauseAfricanbeescomefrom aharsh,drought-strickenlandwhereresources arefew,theyhavebecomeaggressivetoprotectfoodresources.Theyuseanaggressivemobbingstrategy toprotecttheflowerstheyfind.Africanbeeshavebeenknowntomobsmallanimals andstingthemtodeath.Thatishowtheybecamepopularlyknownas“killerbees.”

SincetheintroductionofAfricanbees,honeyproductioninBrazilhasincreasedsix-fold.Some believethis increaseis due tothehigherproductivityoftheAfricanbees.How-ever,thehoped-forhybridofhoneybeesandAfricanbees—a bee that would be both gentleandproductive—hasnotmaterialized.

During the experiments,some African beesaccidentallyescaped.TheAfricanbeeshaveoutcompetedthehoneybeeswhereverthetwospeciesmet.TheAfricanbeeshavesinceexpandedtheirrangenorthwardthroughSouthAmerica,CentralAmerica,andMexicointoTexasandothersouthwesternstates.

Inanotherexampleofintroducingalienspecies,a courtin Brazil recentlyapproved thebreedingofNilecrocodilesata“leatherranch”nearthePantanalRiversystemleadingtotheAmazonRiver.TheNilecrocodileishighlypredatory,responsiblefordozensofhumandeathsinitsnativeAfricaeachyear.Thecrocswere importedto Brazilso theycouldbe raisedto18monthsofage,atwhichtimetheywouldbekilled andskinned. Their skinswould beexportedforthemakingofleatherproducts.Incourt,theimportersarguedthatthesecurityaroundtheranchwherethecrocsarebeingbredisequivalenttothatofa“nuclearinstalla- tion.”

Still,ecologistsare concernedabouttheeffectsonthefragileAmazonecosystemifthisdangerouscrocodilemanagestoescape.TheecologicaleffectsofanuncontrolledpredatorasaggressiveastheNilecrocodilewouldhavecatastrophic impacts onthe Amazonecosystem,alreadythreatenedinmanyplaces.SogreatwouldbetheimpactonthecountlessspeciesoftheAmazon,scientistsarecomparingtheprob-

ableescapeoftheNilecrocto“storingpluto-niuminGrandCentralStation.”

Thecroc’simportersinsistthat“maximumsecurityis[their]mainconcern”andthattheyare “notintroducinganexotic speciesbecause[thecrocodiles]areincaptivity.”TheimportersreportthattheyaretryingtoestablishaleatherindustryinBrazilandmakealiving.Acroco-dilespecialistcounteredwiththeobservationthat ofall the crocodilefarms hehas visited,hefeltthatnonewascompletelysecure.

IntroducingAlienSpeciesforRecreation

Manystatesinournationobtainincomefrom the saleof fishing permitsand from moneyspentbyfishersinlocalcommunities.Topromotesportfishing,thesestatesstocktheirlakes,streams,andriverswithfishspeciesattractivetofishers.Often,however,thesespeciesarenotnativetothatstate.Theirintro-ductionmaydisruptaquaticecosystemsandleadtotheendangermentorextinctionofnativefish.

Federalgovernmentreportsontheeffectsofstockinggamefishindicatethattwo-thirds ofthefishextinctionsthathavealreadyoccurredintheUnitedStateswereduetotheintroductionofalienspecies. Ofthose850nativefishspeciesstillthoughttoexist,morethanone-thirdarenowconsideredrare,near-ingextinction, or possiblyalready extinct. Fullyhalfofthefishonthefederalendangeredspecieslistarebeingoutcompetedbyintro-ducedspecies.

Theeffectsofintroducedspeciesareoftenunforeseen.Forinstance,MontanaintroducedanalienfreshwatershrimpintothetributariesofFlatheadLake,hopingthattheshrimpwouldfattenupgamefish.Theshrimpquicklyspread intothelake,wheretheyconsumedmostofthenativezooplankton. Thisleft littlefood for thenativekokaneesalmon,whichfeedonzoo-plankton.Thesalmonpopulationcrashed,fol-lowedbythebaldeaglepopulation,whichdependsonsalmonasafoodsource.

BenefitsofIntroducingAlienSpecies

Fisheriesmanagersinmoststatesdefendtheir fish-stocking practices.They refutetheargumentofenvironmentaliststhatwaterways

shouldcontainonlynativespecies.Theypointoutthatmostaquaticecosystemshavealready beenalteredandhaveadjustedtothesealter-ations.Managersalsopointoutthat,becausetheyhavetocompetewithotherstatestoattractsportfishers,theyareforcedtostockbodiesofwaterwiththemostsought-afterfish.Themoneythat statescollect fromfishing per-mitsandvacationersiscrucialinmaintainingfisheriesandwildlifeprogramsinmoststates. Withoutthismoneymanystateswouldbeforcedtoseverelycurtailmanagementandpro-tectionofstateparks,wildlifeareas,andwater-ways.

Inadditiontorecreation,theintroductionofforeignspeciescanboosttheeconomyofthe

countrythatimportstheorganisms.TheincreasedproductionoftheAfricanbeesandtheskinsoftheNilecrocodilescanhelpindus-triesprosper.Theseintroducedspeciesmaybenefittheeconomyaslongastheycanbecontainedorcontrolledsothattheywillnotdisrupttheecosystem.

Ifcarefullymonitored,analienspeciesmayhelpreturnthebalanceofanecosystemthatwasdisruptedbysomeothercause.Predatorspeciesmaybeimportedtocontrolapopula-tionofpests.Otherorganismsmaybeintro-ducedtocontrolcertaintypesofpollution.

Whetherornotthealienspeciescanbecon-trolledisanimportantconsideration;accidentalinvaderscanharmanecosystem.

Review

Using Edmodo, answer the following questions in the form of a paragraph.

1.What is an alien species?

2.How do alien species disrupt the balance within an ecosystem?

3.What are different ways that alien species are introduced in to an ecosystem?

4.Select one example of an alien species from the article that you found interesting and describe how it was introduced and the impact it made on the ecosystem.

5.Are there advantages of introducing alien species? If so, explain.

Decisions

In your Edmodo response, choose one of the following topics and provide a response in the form of a paragraph.

1.Ifyouwereastateofficialinvolvedinthemanagementofstateparks,wouldyouapproveofstockingwaterwayswithalienfishspecies?Whyorwhynot?

2.FarmersinthesoutheastUnitedStatesimportedandplantedthekudzuplanttohelpcontrolsoilerosioninthefields.Sincethen,kudzugrowthhasbeenunstoppableandhastakenovermanyagriculturalareas.Recently,however,scientistsfoundthatkudzucontainsasubstancethatisaneffectivetreatmentforpeoplewhoarealcoholdependent.WhatdoyouthinkshouldbedoneaboutgrowingkudzuplantsintheUnitedStatesforthispurpose?

Peer Collaboration

In your Edmodo response, choose one of the following topics and provide a response in the form of a paragraph.

initial response.